As is known in the art, microwave phased array elements which incorporate electronic phase shifters have a wide variety of applications. One such application is in phased array systems. More particularly, beam forming apparatus is used to form beams of electromagnetic radiation. The shape of the beam is related to the phase and amplitude distributions provided to signals received or transmitted across an aperture of the apparatus. For example, in a phased array antenna, the aperture includes a plurality of antenna elements. Each one of the antenna elements is coupled to a feed structure through a corresponding one of a plurality of variable phase shifter-variable gain modules. The feed structure may be a corporate feed or may be through illuminations as in a space fed phased array system. In any event, the modules are controlled by signals from a beam steering computer to provide a collimated and directed beam of radiation. For example, for a broadside (i.e., boresight) beam the phase shift of the signals emanating from each antenna element is zero relative to some arbitrary reference. If the phase shift from element to element differs by a fixed amount from zero, the direction of the main radiation lobe is shifted from broadside accordingly.
When used to transmit radar energy, transmitted pulses have a carrier frequency, fc and each module operates at this same frequency, fc. Thus, for proper operation of the array, there must be a common reference frequency brought to each element through the feed structure.
As is also known in the art, it is desirable to have modules adapted for integrated circuit fabrication. Today, the amplifier sections of the modules are constrained for many applications to be constructed with III-V technology (e.g. GaAs, GaN, InP) materials. The phase shifter portions of the modules are most often monolithically constructed using discrete, switched phase shifters operating at the microwave frequency to be radiated. Recent advances in silicon CMOS technology have enabled implementation of phase shifting functions in an analog manner. Advantages include greater flexibility and lower cost for the phase shifting and frequency control of the array element. One technique suggested is described in an article entitled “Full 360° Phase Shifting of Injection-Locked Oscillators” by Xiangdong Zhang, published in “IEEE MICROWAVE AND GUIDED WAVE LETTERS, VOL. 3, NO. 1, JANUARY 1993. A shortcoming of this technique is the potential for unwanted frequency shift concurrent with beam steering. A further shortcoming is the omission of an efficient and flexible receive path as needed for radar application